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An advanced digital backward-propagation (DBP) method using a separate-channels approach (SCA) is investigated for the compensation of inter-channel nonlinearities in spatial- and wavelength-multiplexed systems. Compared to the conventional DBP, intra-, and inter-mode cross-phase modulation can be efficiently compensated by including the effect of the inter-channel walk-off in the nonlinear step of the split-step Fourier method. We found that the SCA-DBP relaxes the step size requirements by a factor of 10, while improving performance by 0.8 dB for large walk-off and strong linear coupling. For the first time, it is shown that in spatial multiplexed systems transmission performance can be improved by sub-band processing of back propagated channels.

We consider an uplink multi-user scenario and investigate the use of reconfigurable intelligent surfaces (RIS) to optimize spatial multiplexing performance when a linear receiver is used. We study two different formulations of the problem, namely maximizing the effective rank and maximizing the minimum singular value of the RIS-augmented channel. We employ gradient-based optimization to solve the two problems and compare the solutions in terms of the sum-rate achievable when a linear receiver is used. Our results show that the proposed criteria can be used to optimize the RIS to obtain effective channels with favorable properties and drastically improve performance even when the propagation through the RIS contributes a small fraction of the received power., Comment: 5 pages, 4 figures, accepted for publication in IEEE Wireless Communications Letters

5G K-SimSys is a system-level simulator which has been designed and implemented to provide an open platform and a tractable testbed for evaluating the system-level performance of 5G standard. In this paper, we present its design overview with the overall modular structure, including the functionality of the flexible modules. Meanwhile, massive multi-input multi-output (MIMO) is a key technology for improving the spectral efficiency of 5G systems. While massive MIMO has been standardized in 3GPP Rel-13 (LTE-Advanced Pro), the next generation of massive MIMO standard is now available in Rel-16, a.k.a New Radio (NR) interface, with further improvement by introducing more antenna elements over the higher frequency band. In particular, the beam-based air interface for above 6 GHz band involves various antenna configurations and feedback schemes, requiring a more complex testbed for system-level performance evaluation. This paper examines the multi-antenna technologies in 3GPP NR specification to develop its system-level model in 5G K-SimSys in order to test the factors affecting performance in the corresponding environments through various embodiments. In the simulation results, the baseline performance for massive MIMO in NR is evaluated by changing the number of antenna ports and the number of spatial multiplexing layers in different experimental environments. Particularly, the effect of vertical beamforming on interference is evaluated for Full Dimension MIMO (FD-MIMO). In order to demonstrate that 5G K-SimSys is an easy-to-design simulator that facilitates modification and reconfiguration, owing to its modularized and customized structure, we consider the proposed bandwise analog beamforming (BAB) scheme. The modular and flexible structure immediately allows implementation of virtual modules for bandwise analog beamforming by reusing the elementary modules as hierarchically designed simulator objects.

The classic line-of-sight (LoS) MIMO systems optimize antenna spacings according to the communication distance, and the subchannels of fixed symmetric arrays are sensitive with distance variations. Under array aperture constraints, this letter shows that asymmetric array topologies can provide robust spatial multiplexing over a broad distance range. To reduce the implementation costs and power consumption, we further propose to use one-bit quantization for both transmitting and receiving at the terminal of more antennas. Finally, with evaluations using Bussgang decomposition based mutual information lower bound, the proposed one-bit LoS MIMO system is verified with its significant and robust MIMO gain.

As an acute inflammatory response, sepsis may cause septic shock and multiple organ failure. Rapid and reliable detection of pathogens from blood samples can promote early diagnosis and treatment of sepsis. However, traditional pathogen detection methods rely on bacterial blood culture, which is complex and time-consuming. Although pre-separation of bacteria from blood can help with the identification of pathogens for diagnosis, the required low-velocity fluid environment of most separation techniques greatly limits the processing capacity for blood samples. Here, we present an acoustofluidic device for high-throughput bacterial separation from human blood cells. Our device utilizes a serpentine microfluidic design and standing surface acoustic waves (SSAWs), and separates bacteria from blood cells effectively based on their size difference. The serpentine microstructure allows the operating distance of the acoustic field to be multiplied in a limited chip size via the "spatial multiplexing" and "pressure node matching" of SSAW field. Microscopic observation and flow cytometry analysis shows that the device is helpful in improving the flow rate (2.6 μL min-1 for blood samples; the corresponding velocity is ∼3 cm s-1) without losing separation purity or cell recovery. The serpentine microfluidic design provides a compatible solution for high-throughput separation, which can synergize with other functional designs to improve device performance. Further, its advantages such as low cost, high biocompatibility, label-free separation and ability to integrate with on-chip biosensors are promising for clinical utility in point-of-care diagnostic platforms.

In millimeter-wave (mmWave) systems, hybrid precoding/combining architectures are an attractive low-complexity alternative to the use of fully digital precoding. This is because of the reduction in the number of Radio-Frequency (RF) and mixed-signal hardware components. Hybrid precoding/combining design involves a combination of analog and digital processing that enables both beamforming and spatial multiplexing gains in mmWave systems. This paper presents an algorithm for hybrid precoding and combining designs in mmWave systems. The proposed design does not depend on the antenna array geometry, unlike the orthogonal matching pursuit (OMP) hybrid precoding/combining approach. Moreover, this algorithm allows hybrid precoders/combiners to perform close to the known optimal performance of unconstrained digital precoders and combiners. Simulation results verify that the proposed hybrid precoding/combining scheme outperforms the previous methods in the literature in terms of bit error rate (BER) and achievable spectral efficiency with lower complexity.

Analog/digital hybrid beamforming is considered as a key enabling multiple antenna technology for implementing millimeter wave (mmWave) multiple-input multiple-output (MIMO) communications since it can reduce the number of costly and power-hungry radio frequency (RF) chains while still providing for spatial multiplexing. In this paper, we introduce a novel hybrid beamforming architecture with dynamic antenna subarrays and hardware-efficient low-resolution phase shifters (PSs) for a wideband mmWave MIMO orthogonal frequency division multiplexing (MIMO-OFDM) system. By dynamically connecting each RF chain to a non-overlapping antenna subarray via a switch network and PSs, multiple-antenna diversity can be exploited to mitigate the performance loss due to the employment of practical low-resolution PSs. For this dynamic hybrid beamforming architecture, we jointly design the hybrid precoder and combiner to maximize the average spectral efficiency of the mmWave MIMO-OFDM system. In particular, the spectral efficiency maximization problem is first converted to a mean square error (MSE) minimization problem. Then, an efficient iterative hybrid beamformer algorithm is developed based on classical block coordination descent (BCD) methods. An analysis of the convergence and complexity of the proposed algorithm is also provided. Extensive simulation results demonstrate the superiority of the proposed hybrid beamforming algorithm with dynamic subarrays and low-resolution PSs.

Multiple-input multiple-output (MIMO) is a favorable technique that can improve system capacity and performance through spatial multiplexing. However, the performance gets degraded over the correlated wireless channels. In this letter, we consider a point-to-point MIMO system and jointly optimize both the precoding matrix and the difference between two transmit vectors to resist transmit correlation. The simulation results demonstrate that the proposed method can get average 75% gain comparing with the existing method in terms of the minimum pairwise error probability.

Multiple-input multiple-output (MIMO) is a promising technology to efficiently improve the achievable rate of white light-emitting diodes (LEDs) enabled visible light communication (VLC) systems. Nevertheless, for conventional MIMO techniques such as spatial diversity (SD) and spatial multiplexing (SMP), the working mode of each LED transmitter is independent of users' spatial positions. In this article, we propose and investigate three user-centric MIMO techniques, including SD/SMP switching, adaptive SMP (aSMP), and SD-aided aSMP (SD-aSMP), for achievable rate improvement of indoor MIMO-VLC systems, by exploiting users' spatial positions as a new degree of diversity. The analytical and simulation results show that the achievable rate of a 4 × 4 MIMO-VLC system in a typical indoor environment can be significantly improved by applying the user-centric MIMO techniques compared with the conventional ones. More specifically, SD/SMP switching can enjoy both high diversity gain of SD and high multiplexing gain of SMP at different signal-to-noise ratio (SNR) regions, while aSMP mitigates the adverse effect of noise amplification in conventional SMP and SD-aSMP can benefit from additional diversity gain. Furthermore, we also show that the proposed user-centric MIMO techniques outperform conventional MIMO techniques under the condition of only slightly increased computational complexity with limited feedback information.

Fifth generation wireless communication intends to provide extensive improvement in energy efficiency of long-term evolution-advanced network. This feature can be accomplished by incorporating spatial multiplexing which involves base station antenna in large number known as massive multiple input multiple output system. The potential constraint of this system is pilot contamination which introduces interference instigated by reusing pilots from neighbor cells in a multicell system. The pilot contamination can be reduced by varying the length of pilot sequences. The conventional system known as regular pilot uses data and pilot symbols disjointly for transmission. The proposed system known as superimposed pilots overlays the pilot and data symbols for transmission. This superimposed pilot allows to use pilot symbols in an extended duration and in turn reduces the pilot contamination. To analyze the performance of both the pilots, precoding schemes like maximal ratio combing and zero forcing is used. To enhance the performance further antenna selection algorithm has been implemented along with the precoding scheme. This algorithm will choose the antennas with threshold level for maximization of energy efficiency. The simulation results will prove that superimposed pilot with antenna selection algorithm will archive high average rate and energy efficiency than the conventional random pilots.

The design paradigm for backscatter tags is to avoid complex functionality and make tags as simple as possible. However, such a design principle leads to the prevalence of signal collision as tags cannot sense other tags’ ongoing transmissions. The high probability of tag collision will result in low overall throughput. Although there are some existing efforts to resolve tag collisions, they either require good channel conditions or can only resolve a limited number of tags as channel capacity is deficient when SNR is low. In this article, to overcome this limitation, we bring in antenna arrays to boost the channel capacity. We propose FreeScatter, which can support scalable concurrent backscatter transmission using an antenna array. FreeScatter extracts the path that signals traveled and formulates the tags’ channel coefficient using the path representations. FreeScatter further exploits the frequency agnostic property so that it can support more spatial streams than the number of antennas. The experimental results show that we can enable up to 20 tags transmitting concurrently. With the ubiquitous connectivity of battery-free tags in the near future, FreeScatter can significantly boost the network throughput.

This paper proposes a low-complexity and energy efficient sub-connected structure (SCS) hybrid beamforming (HBF) and fully-connected structure (FCS) HBF for non-orthogonal multiple access (NOMA) systems operating under line of sight (LOS) and non-line of sight (NLOS) millimeter wave (mmW) environments. The mathematical model to maximize sum-rate and energy efficiency (EE) of these two HBF-NOMA configurations is formulated to corroborate our simulation results. We aim to maximize both the sum-rates and EEs of the SCS-HBF-NOMA and FCS-HBF-NOMA systems via successive interference cancellation-zero forcing (SIC-ZF) and phased-zero forcing (P-ZF) schemes, respectively. Associated performance analysis under New York University (NYU) mmW channel model is investigated for both two and four users per cluster. It is found that our proposed SCS-HBF-NOMA generally yields higher EE than the FCS-HBF-NOMA in both LOS and NLOS links having high signal to noise ratio (SNR) regime. Moreover, the proposed multistream HBF-NOMA leverages spatial multiplexing to attain higher sum-rates than the single stream counterpart. The employment of $\text{3}\,\text{bit}$ quantization is capable of optimizing the sum-rate for energy efficient finite resolution HBF-NOMA systems. Results also manifest that SCS-HBF structure with reduced antennas in its sub-array beamforms a wider beam capable of mitigating against the performance degradation on the account of channel imperfection in NOMA system. Furthermore, it is found that the number of users per cluster should be carefully selected for optimal performance of HBF-NOMA system. Lastly, space complexity of the HBF-NOMA scheme is found to be the lowest in P-ZF FCS-HBF-NOMA.

Recently, Reconfigurable Intelligent Surfaces (RISs) have drawn intensive attention in the realization of the smart radio environment. However, existing works mainly consider the RIS as a whole uniform plane, which may be unrealistic to be installed on the facade of buildings when the RIS is extremely large. In contrast, this paper investigates a practical Sparse Array of Sub-surface (SAoS) deployment of the RIS for uplink multi-user millimeter Wave (mmWave) communication systems, in which the Mobile Stations (MSs) are distributed in the blind coverage area due to the blockage. In order to exploit the benefits of the sparse deployment, the correlation of the effective channel is firstly investigated. Then the approximation and lower bounds of the ergodic spectral efficiency are derived under frequency and spatial multiplexing scenarios, respectively. Based on the autocorrelation of the effective channel, we obtain an optimal reflect coefficient design as well as the deployment guidelines of RIS tiles. Moreover, the RIS tile scheduling algorithms are also proposed. Numerical results show that the ergodic spectral efficiency approximation matches well with the Monte Carlo result under frequency multiplexing scenarios, and the lower bound is tight under spatial multiplexing scenarios only when the effective channel is strongly correlated. On the basis of the RIS tile scheduling algorithm and the reflect coefficient design, the system performance can be significantly improved under frequency multiplexing scenarios. On the other hand, by deploying more sparse RIS tiles, we can increase the multiplexing gain under spatial multiplexing scenarios.

How to reduce the hardware cost and high power consumption of RF link of communication device is the key problem to be solved for multi-transmitting antenna and multi-receiving antenna system (MIMO). Always choose the best antennas connection a limited number of RF circuits, which is called antenna selection technology (AS), are a perfect solution to the problem, Assuming that the spatial range of the antenna meets the requirements of signal multiplexing and based on the maximum capacity criterion of the selected MIMO system, the manuscript proposes a low computational complexity (CC) and high performance joint transmitting and receiving antenna selection technique (JTRAS). Starting from the traditional capacity formula and the full matrix of MIMO channel, we utilize a simplified channel capacity expression through repeatedly iterating to delete a row and a column of the equivalent decrement channel matrix, which is to remove a pair of transmitting and receiving antennas. Based on the decreasing JTRAS (DJTRAS) algorithm, the capacity results of simulating calculation indicate that its median capacity overtakes other ones, such as optimum selection (OS), AS based on Frobenius 2 norm (NBS), and concise joint AS criterion (CJAS) etc., and the novel DJTRAS scheme can significantly reduce computational complexity (CC) compared to the exhaustive search method with maximum capacity, which defined as optimal algorithm in the curve graphs. This new technology of the AS is particularly suited to large number of selected antennas, such as Lt ≥ NT /2,Lr ≥ NR /2.

Increasing usage of wireless communication systems and demand for higher data speed is appealing newer generations of cellular communication systems to provide higher data rate along with a reliable system, i.e. system which is free from interference. 5G Communication systems are believed to provide at least ten times betterment in area throughput, i.e. data rate by increasing the spectral efficiency. Massive MIMO (multiple-input multiple-output) is a key 5G technology that uses massive antenna arrays to provide a very high beamforming gain and spatial multiplexing of users and hence increases the spectral and energy efficiency. However, although Massive MIMO suppresses intra-cell interference and uncorrelated noise to a significant amount, it cannot mitigate the Pilot Contamination (PC) which is caused by reusing the same set of pilot signals in adjacent cells. In this paper, a new Pilot Decontamination (PD) technique, named as Softly Reused Pilot Weighted Graph Coloring-based Pilot Decontamination (SRPWGC-PD) has been introduced. In the proposed scheme, a scheme named soft pilot reusing is applied to separate the users in cells into two (inner and outer) zones, and then outer-zone users are allocated with orthogonal pilots; whereas a special pilot allocation scheme named weighted graph coloring algorithm is applied to the inner zone users to make generated PC as less as possible. Simulation and numerical analysis provide an insight that the proposed scheme outperforms in most of the performance indices, when compared to the existing schemes reported in the literature.

Degree-of-freedom (DoF) based models have become prevalent in studying MIMO-based wireless networks. However, most existing DoF-based models assume the channel matrix is of full-rank. Such a simplifying assumption has gradually become problematic, particularly when the number of antennas increases and the propagation environment is not close to ideal. In this paper, we address this problem by developing a general theory for the DoF-based model under general channel rank conditions. We start with a fundamental understanding on how MIMO’s DoFs are consumed at each node for spatial multiplexing (SM) and interference cancellation (IC) in the presence of rank-deficient channels. Based on this understanding, we develop a DoF model that can be used for identifying the DoF region of a multi-link MIMO network and for studying DoF scheduling in MIMO networks under general channel rank conditions. Specifically, we find that for IC, shared DoF consumption at both transmit and receive nodes is critical for efficient DoF allocation. Further, we show that DoF consumption under the existing full-rank assumption is a special case of our generalized DoF model. Based on case studies, we show that the general IC model can achieve larger feasible DoF regions or improved objective values than existing unilateral IC models. The findings of this paper pave the way for future research of many-antenna networks under general channel rank conditions.

Millimeter-wave (mm-wave) multi-input–multi-output (MIMO) systems with the digitization of every element enable spatial multiplexing, virtual arrays for radar, and digital beamforming for high mobility scenarios. However, per-element digitization results in a formidable I/O challenge in large-scale tiled MIMO mm-wave arrays. This article analyzes a code-domain approach to multiplex signals from different elements as well as the LO on a single interface. System considerations are presented, and the approach is demonstrated through a 28 GHz four-element MIMO receiver in 65-nm CMOS. Measurements show the feasibility of digital beamforming after de-multiplexing of the baseband signals from the IF/LO interface. Each element in the array achieves 16-dB conversion gain while consuming 60 mA from 1.2 V. The IC occupies 5.75 mm2 in 65-nm CMOS, achieving small size and compatibility with $\lambda /2 \times \lambda /2$ antenna spacing due to the absence of phase shifters/combiners required in phased arrays.

Spatial multiplexing multiple-input multiple-output (MIMO) visible light communication (VLC) has become a potential candidate for next-generation wireless communication networks. In this paper, a novel superposed odd-order 32QAM constellation scheme is proposed in 2 × 2 MIMO VLC systems. Two independent signals generated from two light emitting diode (LED)-based transmitters with a four-quadrature amplitude modulation (4QAM) and geometrically shaped square 8QAM, respectively, are transmitted over free space and spatially multiplexed in the receiver to obtain a distinctly square-shaped 32QAM signal. The high channel correlation causes failure of MIMO detection in traditional spatial multiplexing (SMP) systems owing to the rank defect of the channel matrix. However, MIMO detection can always be realized by a simple constellation de-mapping based on the concept of superposed constellations, regardless of the extent of channel correlation. Considering the non-linearity of an LED, the square-shaped 8QAM constellation is introduced to reduce the peak to average power ratio (PAPR) at the transmitter, which also benefits from its maximum minimum Euclidean distance (MED) at the receiver compared to those of traditional 8QAM constellations. Moreover, the equal-gain combining (EGC) algorithm is employed to gain the receive diversity. The proposed system is experimentally studied in detail, where the system performance is evaluated under the conditions of different driving peak-to-peak voltages (Vpps) and channel gains. The experimental demonstration also shows that the dynamic range of the driving Vpp can be improved from 0.3 V to 0.6 V when compared with that of the traditional non-geometrically-shaped 8QAM, clearly validating the superiority of the proposed system.

Generalized frequency division multiplexing (GFDM) is a prominent candidate to be used by the mobile Fifth Generation (5G) physical layer. Nevertheless, the integration of GFDM with Spatial Multiplexing (SM) MIMO system is essential to fulfill the data rate requirements. SM detection of MIMO-GFDM becomes a more challenging topic because of ICI and ISI due to the non-orthogonal nature of GFDM, along with IAI. In this article, the authors propose a system that combines the Offset-Quadrature Amplitude Modulation (OQAM) with GFDM to mitigate self-induced interference, by using a simple Matched Filter (MF) detector and minimum additional processing at the receiver. Simulation results show a considerable achieved improvement in BER by the proposed OQAM/GFDM compared to QAM/GFDM when using MMSE-based Ordered Successive Interference Cancellation (OSIC) detector. Furthermore, this system is unaffected by the roll-off factor variations of used pulse-shaping filters.

Hybrid beamforming antenna arrays are a prominent component in communications at millimeter-wave frequencies. Multiple analog beamforming arrays will be used for spatial multiplexing of signals also in hand-held devices. In this letter, we derive the correlation coefficient for signals received by two ideal arrays in simple power angular distribution schemes. The purpose is to develop tools for evaluating over-the-air (OTA) setups for testing of hybrid beamforming devices. We show a few exemplary correlation error evaluations that compare near-field multiprobe OTA setups with a perfect target channel model. Results indicate that the correlation error increases with decreasing range length and channel angular spread. Moreover, larger interarray spacing and subarray sizes increase the correlation error.

MIMO spatial multiplexing is an essential feature to increase the communication data rates in current and future cellular systems. Currently, the ns-3 lte module leverages an abstraction model for 2x2 MIMO with spatial multiplexing of two streams; while mmwave and nr modules were lacking the spatial multiplexing option until this work, since the ns-3 models were not supporting the usage of multiple antennas for spatial multiplexing and an abstraction model such as the one used in the lte module is not suitable for the mmWave frequencies. In this paper, we propose, implement and evaluate models for ns-3 and the nr module to enable Dual-Polarized MIMO (DP-MIMO). The proposed extension for the ns-3 supports multiple antennas for DP-MIMO with spatial multiplexing of two streams and can be used by any ns-3 module that is compatible with the ns-3 antenna array-based models, such as nr and mmwave modules. We leverage this ns-3 extension to model DP-MIMO by exploiting dual-polarized antennas and their orthogonality under line-of-sight conditions, as it happens at high-frequency bands, to send the two data streams. The proposed model does not rely on abstraction, as the MIMO model in the ns-3 lte module, and can thus model more realistically the propagation differences of the two streams, correlation, inter-stream interference, and allows design and evaluation of the rank adaptation algorithms. Additionally, we propose and evaluate an adaptive rank adaptation scheme and compare it with a fixed scheme. The developed DP-MIMO spatial multiplexing models for the ns-3 simulator and the nr module are openly available.

International audience; In order to meet the energy efficiency requirements of future wireless communication systems, we propose in this paper a joint switched beamforming and user pairing scheme. We designate by switched beamforming the process of choosing between non-orthogonal multiple access (NOMA) and spatial multiplexing as the beamforming scheme for a group of users. In this context, we formulate the power minimization problem subject to the quality of service (QoS) constraints and pairing constraints for a multiple-input single-output (MISO) communication system. In order to solve the nonconvex optimization problem, we propose a two-step solution. Firstly, given a group of users, we provide an efficient method to compute the optimal beamformers using semidefinite relaxation. Then, we propose an algorithm to determine the optimal pairing strategy and the optimal beamforming scheme for each group. Results reveal that the proposed scheme outperforms NOMA and spatial multiplexing, confirming the importance of exploiting the switched beamforming problem and the user pairing problem jointly to minimize the power consumption. Particular attention is thus paid to the assessment of the impact of the number of antennas on the choice of the beamforming scheme.

This paper considers advanced techniques for multiple-input multiple-output (MIMO) detection and decoding techniques to improve bit error rate (BER) and channel capacity. These are requirements for sixth generation (6G) (the next generation) access networks. A parallel decoding and detection scheme and a soft bit decoding scheme are implemented meregely to boost the overall performance of MIMO communication systems. The proposed new system is called the advanced system which comprises the two mentioned advanced techniques of decoding. For simplicity, these advanced techniques are employed and developed using two antennas at both ends, transmitter, and receiver. Then it is compared with the other different techniques which are spatial multiplexing SM–sequential decoding zero forcing-interference cancelation (ZF-IC) technique and SM–parallel decoding technique. We show that the advanced system outperforms the other two mentioned systems by achieving ultra-reliability and a high capacity simultaneously without employing space time coding and error control coding techniques. Additionally, better BER performance is achieved with less resolution and the quantization error reduced with an increasing the resolution. The new advanced system is simulated and evaluated with three terms, channel capacity, BER, and quantization error.

In this paper, a 4×4 fixed-scale multi-input multi-output (MIMO) underwater optical wireless communication (UOWC) system is implemented with spatial multiplexing to achieve 20 Mbps rate over 2-m link distance which consists of 1-m free space and a 1-m water-filled tank. Experimental results suggested that the fixed-scale MIMO UOWC system shows more robustness than the conventional counterpart against our experimental setup.

Multi antenna transmission and reception is included in last-generation and future wireless communication standards, such as DVB-T2 or DVB-NGH, to increase bandwidth efficiency and receiver robustness. The primary goal is to combine diversity and spatial multiplexing in order to fully exploit the capacity of multiple-input multiple output (MIMO) channels. For this purpose, full-rate full-diversity (FRFD) space-time codes (STC) such as the Golden code are being investigated. Despite their higher achievable capacity, most of them have a high soft detection complexity, which prevents them from being combined with soft-input decoders in bit-interleaved coded modulation (BICM) schemes. This paper presents a study of a low complexity soft detection algorithm for receiving FRFD space-frequency block codes in BICM orthogonal frequency division multiplexing (OFDM) systems and compares performance using LDPC and Turbo codes. The proposed detector has a low and fixed complexity, avoiding the variable nature of the list sphere decoder (LSD), which is dependent on noise and channel conditions. The proposed detector performs close to the optimal log-maximum a posteriori (MAP) detection in a variety of DVB-T2 broadcasting scenarios, according to complexity and simulation-based performance results.

Superposed constellation combined with spatial multiplexing multiple-input multiple-output (MIMO) techniques have been increasingly utilized in visible light communication (VLC) systems, as multiplexing gains can be achieved regardless of the correlation extent of the VLC channel. Herein, we propose a novel superposed 64-quadrature amplitude modulation (QAM) constellation scheme for 2 × 2 MIMO VLC systems. Considering the nonlinearity of light-emitting diodes (LEDs), two geometrically shaped 8QAM constellations are introduced to reduce the peak-to-average power ratio at the transmitter. Because the two 8QAM constellations are superposed in an interleaved manner, the required power ratio between two transmitted signals is 1, which further reduces the risk of nonlinear distortion and avoids signal-to-noise ratio deterioration induced by power competition. The proposed superposed 64QAM constellation scheme is experimentally investigated comprehensively, where the system performance is evaluated under different transmitted powers, direct current bias currents, and driving peak-to-peak voltages (Vpps). The experimental results show that the proposed scheme achieves better bit error rate (BER) performance than the traditional superposed 64QAM constellation schemes. Below the 7% pre-forward error correction BER threshold of 3.8 × 10−3, the dynamic range of the driving Vpps of the two LEDs improves from 0.06 to 0.4 V and 0.23 to 0.4 V when the optimal power ratio is achieved.

Since there has been a rapid rise of cell phone customers in the data communication system, the cell phone clients require excessive attributes like enhance data rates, traffic, and reliable transmission of data. Suppliers have the responsibility to fulfill all the needs of customers that can be majorly done with the usage of upcoming generation i.e. fifth-generation (5G) telecommunication. This forthcoming technology offers a very large bandwidth, a better quality of service (QoS), appropriate capacity, minimizes the latency period, and enhanced spectrum. Small cell base stations (SCBS) and diverse antennas are perceived as a basic technology in the exposure of the future generation 5G. The usage of several antennas in traditional telecommunications central stations has already been widely studied. However, due to diversification in the present complex network and development of this subject with the more densification predicted in the upcoming 5G network, their usage in SCBS is at a progressive phase. This paper demonstrates a broad survey of areas in which it uses as well as challenges employed while using these diverse antennas in SCBS and different designs of antennas are considered with its challenges while being employed in terms of its measurements, performance, and price. This paper states that the various guidelines to use these diverse antennas according to their classifications in small cells as it is a presiding technology required for future generations i.e. 5G.

In a dense 5G urban-eMBB environment, the user density and traffic loads follow a spatio-temporal variability. To meet high traffic demands, the 5G base stations exploit spatial multiplexing by means of Active Antenna Systems (AAS) and beamforming. However, pedestrian and vehicular users are highly mobile, rendering non-dynamic beamforming designs totally inefficient in terms of meeting the users' demand requests. In particular, the latter results in either overload or underutilized beams in a cell. Hence, a practical approach to meet such spatio-temporal heterogeneous demand is to consider dynamic and adaptive beam footprint design that takes into account both the actual users' position as well as the traffic loads. In this paper, we first study and evaluate the state-of-the-art fixed-cell beamforming (based on ITU-R M.2412-0) in a test environment and highlight its drawbacks. Next, we propose a adaptive macro-cell beam footprint design where the beams are dynamically shaped based on the spatial users distribution and their demand requests. Numerical simulations demonstrate the high system performance achieved by the proposed methodology.

In general, realization of large array communication for mm Wave systems is non-vital. Radio Traditional digital antenna array that comprises of one Radio Frequency (RF) chain for every antenna leads to high consumption of energy, complexity in signal processing, residue of noise. However, one major drawback of analogue beam forming lies in its inability to support spatial multiplexing. Minimum Variance Distortion less Response (MVDR) is enhanced to rectify this noise inference and also the variance/power of interference. The major aim of this work is to maximize the MVDR and minimum Signal-To-Interference-Plus-Noise Ratio (SINR through effective designing of beamforming and optimal selection of antenna. Antenna selection based on power is proposed at first step and beamforming vector is optimized after selection of antenna as like in single-user setup. In case of impossibility of separation of multi-path signal, performance is enhanced by an Improved Group based Particle Swarm Optimization (IGPSO) based antenna selection and Joint adaptive beamforming scheme is proposed. A Beamforming coefficient of the entire user’s associated with an antenna is assigned to zero by MVDR and SINR in order to deactivate certain antenna. So, IGPSO is deployed in design of beamforming and joint selection of antenna. It has a non-convex constraint. Convex constraint is used for effectively approximate it. Experimental results shows that proposed design including array of lens antenna is able to produce better performance than benchmark schemes with reduced Bit Error Rate (BER) and improved spectral efficiently in terms of Spectrum efficiency and max min rate.

For multiple active spatial modulation (MASM) technique, this letter formulates the minimum number of transmit antennas $(N_{\mathrm {t}})$ and the required number of active RF chains ( $N_{\mathrm {a}}$ ) to support the following two statements. First, it is proven that MASM can achieve similar spectral efficiency to conventional spatial multiplexing (SMx) with smaller $N_{\mathrm {t}}$ and $N_{\mathrm {a}}$ , and less receive antennas ( $N_{\mathrm {r}}$ ). Secondly, for operation with the same $N_{\mathrm {t}}$ in both techniques, MASM is shown to achieve higher spectral efficiency while using fewer $N_{\mathrm {a}}$ and $N_{\mathrm {r}}$ . Furthermore, the low spectral efficiency and diversity tradeoff in MASM is highlighted, and a proposal of an enhanced MASM (E-MASM) technique is shown to achieve a better tradeoff between spectral efficiency and diversity as compared to SMx. In comparison to SMx and some prominent space modulation techniques, E-MASM is shown to achieve higher reliability, while MASM achieves superior spectral efficiency.

Spatial multiplexing using orbital angular momentum (OAM) modes is an efficient means of scaling up the capacity of fiber-optic communications systems; integrated multiplexers are crucial enablers of this approach. OAM modes are circularly polarized when propagating in a fiber, however, OAM generators previously demonstrated in silicon photonics use locally linearly polarized emitters. Coupling from multiplexers to fibers in those solutions results in extra loss and complexity. Moreover, many of those solutions are based on resonator structures with strong wavelength dependence, and are thus incompatible with wavelength-division multiplexing (WDM). We experimentally demonstrate on-chip generation and multiplexing of OAM modes using an array of circularly polarized 2-D antennas with wide wavelength coverage. The proposed device was implemented on the standard 220-nm silicon-on-insulator platform. Optical vortex beams with OAM orders ranging from −3 to +3 in both left and right circular polarization states were generated from the same aperture across a wavelength range of 1540 to 1557 nm. This device could serve as a multiplexer or demultiplexer for up to 12 information bearing channels coupling into an OAM fiber, and is compatible with WDM multiplexing as well.

In this paper, an $M\times 4$ double space-time line code (D-STLC) is designed for a system with $M$ -transmit and four-receive antennas whose channel state information is available at the transmitter. By delivering two independent STLC data streams simultaneously, both spatial diversity and multiplexing gains are obtained, like a $4\times M$ double space-time transmit diversity (DSTTD) system that transmits two space-time block coded data streams. It is analytically shown that the decoding signal-to-interference-plus-noise ratios of D-STLC and DSTTD are identical to each other, and furthermore, it is numerically verified that the proposed D-STLC significantly outperforms a conventional $M\times 4$ STLC scheme and other existing spatial-diversity and spatial-multiplexing schemes, such as precoded space-time block code and precoded spatial multiplexing, in terms of achievable rate and bit-error-rate performance as the signal-to-noise ratio and/or transmission data rate increase.

The offering of demanding telecommunication services as promised by the 5G specifications raise the necessity for high capacity, flexible, adaptive, and power conserving fronthaul. Toward t...

To support multiple users in an indoor multiple-input multiple-output visible light communication (MIMO-VLC) system adopting spatial multiplexing, orthogonal frequency division multiple access (OFDMA) is usually adopted, where the overall modulation bandwidth is shared by all the users. In this paper, by fully exploiting the spatial distributions of light-emitting diode (LED) transmitters in the ceiling and end users around the receiving plane, we propose a space division multiple access (SDMA) technique for indoor spatial multiplexing-based MIMO-VLC systems. When applying SDMA, users within the MIMO-VLC system are divided into different user groups (UGs) based on their spatial locations with respect to different LED transmitters. Specifically, each UG can use the overall modulation bandwidth of the system. For efficient implementation of SDMA, two distributed user grouping (DUG) approaches are proposed, including basic DUG and transmit diversity-enhanced DUG (TD-DUG), and a two-step resource allocation algorithm is further designed. The achievable rates of the MIMO-VLC system employing SDMA with both basic DUG and TD-DUG are derived accordingly. To verify the superiority of SDMA over conventional OFDMA, detailed analytical and simulation results are presented. Moreover, a proof-of-concept experiment is conducted to demonstrate the advantage of SDMA in a practical spatial multiplexing-based MIMO-VLC system.

Multiple-input multiple-output visible light communications (MIMO-VLC) have been considered as an advanced technique owing to the enhancement of communication capacity and reliability. However, the performance of MIMO-VLC highly depends on channel correlation, which means that the system performs worse when the channels are more highly correlated. Some studies have developed techniques to alleviate channel correlation and improve the performance of spatial multiplexing MIMO-VLC systems. However, these works have not considered situations where all LEDs and PDs are integrated into a compact structure. In this paper, a single-user spatial multiplexing MIMO-VLC system with densely distributed LEDs (light emitting diodes) and PDs (photodiodes) is proposed. Designs of optimal signal vectors and system structures are introduced, to fulfill multiplexing gains when LEDs and PDs are set close to each other respectively. Numerical simulations are carried out and the results illustrate that the proposed system can realize multiplexing gains over the system where LEDs and PDs are distributed densely, and also outperforms the traditional repetition coding (RC) technique.